1. Field of the Invention
The present invention relates to transmitter, receiver and transceiver apparatus.
2. Description of the Related Art
In our International patent application PCT/GB97/03472 and our British patent application 9726873.4, the entire disclosures of which are incorporated herein by reference, there is disclosed a communications apparatus comprising a mesh of interconnected nodes. Each node can communicate with plural other nodes via point-to-point radio links between nodes by means of substantially unidirectional radio transmissions along the links, i.e. signals are not broadcast but are instead directed to a particular node with signals being capable of being passed in both directions along the link. Each node has plural links to other nodes, for example eight links, providing a connection from each node to eight other nodes. In an example, time division duplex (TDD) is used to alternate transmission and reception nodes along a link. In a preferred embodiment, time division multiplexing (TDM) is used to control the timing of transmission and reception between the links. For example, a node is able to transmit along a first link in a first time slot of a transmission portion of a time frame, along a second link during the second time slot of the transmission portion of the time frame, etc., for eight transmission time slots for the eight links. The node then is able to receive along the first link during a first time slot of the reception portion of the time frame, along the second link during the second time slot of the reception portion of the time frame, etc., for eight reception time slots for the eight links. As an alternative to TDD, frequency division duplex (FDD) or other techniques may be used.
Because the radio components of a transceiver are relatively expensive, it was proposed in PCT/GB97/03472 and British patent application 9726873.4 to provide a single radio subsystem at each node with a M-way-switch to switch the radio subsystem between the M links of that node.
Because the links between nodes in the communications apparatus disclosed in PCT/GB97/03472 and British patent application 9726873.4 are point-to-point using substantially unidirectional transmissions for transmission and reception on a link, i.e. signals are not broadcast but are instead directed to a particular node with signals being capable of being passed in both directions along the link, it is important that the antennas of linked nodes be properly and accurately aligned so that transmission from one node to a linked node is properly and completely received. Alignment of the antennas is in practice difficult, especially as the linked node may be a kilometre or more apart from each other. In principle, the nodes to which a particular node is linked may be located in any direction. The number of nodes to which a particular node is linked is also initially unknown. Furthermore, new nodes in any arbitrary location nay be added to the communication apparatus at any time as the communication apparatus develops.
Accordingly, it is beneficial to be able to provide substantially 360xc2x0 azimuthal transmission and reception coverage at each node and then select only particular directions for actual transmission/reception links with other nodes. This can be achieved by providing more antennas at each node than there are links at that node. For example, where eight links to and from a node are required, it may be convenient to provide thirty-two antennas which together provide 360xc2x0 coverage in a substantially horizontal plane. For each link direction, at least one of those thirty-two antennas is likely to be facing in the appropriate direction so that particular antenna can be selected for providing a transmission/reception link with a neighboring node.
The problem with providing many antennas at a particular node is that the cost of the switch that is used for switching between the antennas becomes significant. The performance of the switch can also suffer when it is expected to switch between many antennas. This is particularly the case at the high frequencies contemplated for the communication apparatus disclosed in PCT/GB97/03472 and British patent application 9726873.4 in which frequencies of 1 GHz or higher such as 2.4 GHz or 4 GHz or 40 GHz or 60 GHz or 200 GHz or higher are proposed. Also, at these high frequencies, it is important that the apparatus be as small as possible, with the radio components being positioned close to the antennas in order to minimize losses in the couplings.
Accordingly, there is a need for apparatus which provides multiple antennas in which the radio components can be positioned close to the antennas and which provides for switching between the multiple antennas at low cost but with high performance.
According to a first aspect of the present invention, there is provided transmitter apparatus, the apparatus comprising: a plurality of sets of substantially unidirectional antennas; each set of antennas having a single radio subsystem for providing a radio output signal for transmission by one of the antennas in the set; each of the plurality of radio subsystems having a switch for switching the output of the radio subsystem to a selected one of the antennas in the set to which the radio; subsystem is connected for transmission of a radio signal output by the radio subsystem from said selected antenna.
According to a second aspect of the present invention, there is provided receiver apparatus, the apparatus comprising: a plurality of sets of substantially unidirectional antennas; each set of antennas having a single radio subsystem for receiving a signal received by one of the antennas to provide an output signal from the radio subsystem; each of the plurality of radio subsystems having a switch for switching an input of the radio subsystem to a selected one of the antennas in the set to which the radio subsystem is connected such that a signal received by said selected antenna is passed as an input to the radio subsystem.
According to a third aspect of the present invention, there is provided transceiver apparatus, the apparatus comprising: a plurality of sets of substantially unidirectional antennas; each set of antennas having a single radio subsystem for providing a radio output signal for transmission by one of the antennas in the set and for receiving a signal received by one of the antennas to provide an output from the radio subsystem; each of the plurality of radio subsystems having a switch for switching the output of the radio subsystem to a selected one of the antennas in the set to which the radio subsystem is connected for transmission of a radio signal output by the radio subsystem by said selected antennas and for switching an input of the radio subsystem to a selected one of the antennas in the set to which the radio subsystem is connected such that a signal received by said selected antenna is passed as an input to the radio subsystem.
The present invention in its various aspects allows radio subsystems to be shared between multiple antennas, keeping down the costs, whilst allowing each radio subsystem to be positioned close to the antennas which are served by that radio subsystem. At the same time, the number and complexity of the switches is also optimized to keep down costs whilst ensuring high performance. In the third aspect, each radio subsystem may be arranged to switch between reception and transmission modes using time division duplex.
At least one of the radio subsystems may be arranged to operate at a first frequency for signals input to the radio subsystem from the antennas and at a second frequency for signals output by the radio subsystem to the antennas. Said at least one radio subsystem may be arranged to receive and transmit signals substantially simultaneously.
In any of the aspects mentioned above, the antennas are preferably arranged to provide 360xc2x0 azimuthal coverage. This greatly facilitates set-up and maintenance of radio transmission links between apparatus according to the present invention.
The antennas are preferably arranged in a circular array in which all of the antennas are directed away from common origin. Again, this greatly facilitates set-up and maintenance of radio transmission links between apparatus according to the present invention.